Representation methods of this kind and the corresponding objects are known.
Thus, for example, a representation method of this kind is known from the technical article “Quantitative Analyse von koronarangiographischen Bildfolgen zur Bestimmung der Myokardperfusion” (“Quantitative analysis of coronary angiographic image sequences for determining myocardial perfusion”) by Urban Malsch et al., published in “Bildverarbeitung für die Medizin 2003—Algorithmen—Systeme—Anwendungen” (“Image processing for medicine 2003—algorithms—systems—applications”), Springer Verlag, pages 81 to 85. With this representation method a computer determines a two-dimensional evaluation image comprising a plurality of pixels on the basis of the projection images and outputs the evaluation image to a user via a display device. The pixels of the evaluation image correspond to those of the projection images. Based on the variation over time of the pixel values of the projection images, the computer assigns a pixel value to the pixels of the evaluation image, the pixel value being characteristic of the time of the maximum change in contrast.
The teaching of the above-cited technical article is described in the context of angiographic examinations of the coronary vessels of the human heart. This type of examination is one of the most important diagnostic tools in cardiology today. Additional information such as determining the flow rate or myocardial perfusion is further information which can be obtained in principle by means of angiography. The essential diagnostic finding is the perfusion of the myocardium.
Further noninvasive examination methods such as PET, SPECT, MR or contrast-medium-based ultrasound are known in the prior art. In addition to other parameters, these examination methods also enable the perfusion status of the myocardium to be quantified. These methods are generally applied in stable angina pectoris cases or for risk assessment following a myocardial infarction.
For an assessment of the therapeutic outcome of an intervention it would be advantageous to be able to monitor the improvement in perfusion or, as the case may be, the occurrence of microembolization and microinfarctions during the actual intervention. It would therefore be advantageous if a quantification of the perfusion were added to other diagnostic parameters already in the catheter laboratory, as this would enable all the relevant information to be obtained in one examination and thus to achieve an improvement in the monitoring of treatment.
However, quantifying the perfusion of the myocardium using angiographic methods is problematical, since the angiographically observable cardiac vessels have a diameter of barely a millimeter or more. These observable vessels terminate in millions of tiny capillary vessels which have diameters of only a few micrometers. The flow dynamics and distribution in the capillary vessels are ultimately determined by the blood supply of the cardiac muscle. Drawing conclusions about the dynamics of perfusion in the capillary vessels from the macroscopic perfusion is therefore, strictly speaking, inadmissible, even though it is often practiced.
Various methods for recording the perfusion of the myocardium are known, in particular contrast echocardiography, magnetic resonance tomographic diagnostics and SPECT.
The echocardiographic determination of global and regional function is an integral component of noninvasive cardial functional diagnosis. Dynamic and pharmacological stress echo cardiography are used in particular in cases of ischemia and in vitality diagnostics and contribute toward indicating revascularizing measures in the case of chronic coronary heart diseases. Recently introduced contrast-specific imaging methods enable the signal from the intramyocardial blood pool to be amplified and on the basis thereof deductions can be made with regard to the myocardial perfusion. Current realtime methods even enable the simultaneous assessment of wall motion and myocardial perfusion at a high spatial resolution.
Magnetic resonance tomographic diagnostic methods for coronary heart diseases are based on the evidence of pharmacologically induced perfusion or wall-motion disorders. Contrast-medium-based first-pass perfusion measurement at rest and under pharmacological stress is the preferred procedure today for assessing myocardial perfusion. Here, drugs are used which lead to dilation of the unaffected coronary arteries and consequently, due to the raised blood flow in these dilated coronary arteries, result in an increase of the lower perfusion rate in the area supplied by a stenosed coronary artery.
SPECT is a nuclear medicine technique. Tc-99m is nowadays used for this purpose as a contrast medium in addition to thallium-201 chloride. Myocardial perfusion scintigraphy records the perfusion of the cardiac muscle under ergometric and pharmacological stress and at rest. In the process reversible ischemias can be differentiated from permanent perfusion disorders or myocardial scars. A prerequisite for this method is an optimized tomographic examination technology.
Acute myocardial infarction represents a cardiological emergency situation in which rapid diagnosis and treatment are required. In this type of emergency situation an examination of the patient using magnetic resonance tomographic methods, SPECT methods or contrast echo cardiography is generally not possible. Further problems arise if for different reasons it was not possible to carry out a perfusion measurement in advance. In all these cases angiographically based cardiac perfusion imaging would represent an important tool.
In angiographically based cardiac perfusion imaging, long recordings are made, the recordings lasting until such time as the contrast medium has flowed through the coronary vessels and is visible in the myocardium itself. This last-mentioned phase is referred to as “myocardial blush”. Assessment of the “myocardial blush” serves to provide evidence of the vascular supply to the heart and for example to rate the success of treatments and/or a risk profile for the patient.
In order to make the blood flow dynamics in large vessels and in the capillary vessels measurable and thereby comparable, various gradation systems are known which divide up the continuum of conditions into discrete classes. Some of these classifications describe the macroscopic circulation of blood, others the circulation of blood in the capillaries. The most-used classifications were drawn up by the scientific organization “Thrombolysis in Myocardial Infarction” (TIMI). These classifications are regarded as the de facto standard. The TIMI classifications are frequently used in multi-center studies in which the primary objective is to obtain reproducible and comparable results. However, the classifications are complex and time-consuming to apply. They are therefore not generally used in routine clinical work.
By far the most frequently used method in the prior art is visual assessment of the “myocardial blush” on the screen. This procedure is often used for multi-center studies. A prerequisite for this procedure is that the angiographic recording is long enough in order to be able to see the entry and washout of the contrast medium. However, the visual assessment requires a great deal of experience and is in practice carried out only by TIMI blush experts, as they are known.
There are also various procedures known in which an attempt is made to carry out the subjective-personal visual assessment with the aid of computers. An example can be found in the above-cited technical article by Urban Malsch et al.
The procedure in the above-cited technical article represents a good initial approach but still has shortcomings. Thus, for example, it is necessary in particular to identify the vessels of the vascular system in the projection images in order to mask out these vessels when analyzing the “myocardial blush”. With the procedure presented in the technical article it is also necessary to work with DSA images. This creates a significant risk of artifacts, so that compute-intensive motion compensation methods are in turn required in order to avoid said artifacts.
Image evaluation methods for two-dimensional projection images are also described in the German patent application DE 10 2005 039 189.3. On the day of filing of the present invention the cited patent application is not yet publicly accessible and therefore does not represent a general prior art. This patent application is to be taken into account in the process of the examination as to novelty only in the German patent granting procedure.
The approach disclosed in DE 10 2005 039 189.3 is already very good. The color-coded representation of the parcel type (vessel, perfusion region, background) and the extent (degree of perfusion) also results in a good detectability of the perfusion determined in the context of DE 10 2005 039 189.3. On the other hand, the approach described in DE 10 2005 039 189.3 is not suitable for direct detectability of the perfusion of the examination subject, in other words for the visual assessment of the blush.